My attempts to make a rapid prototyping machine that I will use to make parts for a machine that will be able to make parts for a copy of itself.

Saturday, 24 April 2010

ABS on PET tape

I find ABS sticks to Kapton very well to start with, but as it ages, it seems to stick less well. Corners start to lift and eventually builds are ruined. I have tried cleaning it with isopropyl alcohol and with acetone but it makes no difference. Charles Pax has reported that sanding with 220 grit paper makes it stick better. I cannot reproduce this. In fact, I find the opposite effect. It always sticks well when new, and if anything, sanding it makes it worse.

Somebody pointed out a while ago that you can get PET tape that is rated to 250°C. That is not as high as Kapton, but just about adequate for a heated bed when extruding ABS at 240°C.

I bought some and when my Kapton stopped working I decided to give it a try. It seems to work well. The first layer goes down perfectly :-

and the objects stay flat: -

I do the first layer at 240°C with the bed at 120°C and subsequent layers at 220°C with the bed at 110°C. I have made all the parts for an extruder on it so far and it has performed perfectly. The extruder will be on eBay this evening.

It is too early to say if it better than Kapton, but it looks promising.

Yes there is a limit to how big we can make things without a heated chamber. It is much bigger with PLA of course.

Extruding at a higher temperature and with a bigger width / height ratio will help for bigger objects.

I have don't know if PET will age as I have no idea why Kapton ages. I think the adhesion on a shiny surface is a combination of Van de Waals forces and suction.

Jordan Miller has also told me that PLA sticks to warm glass, which is 100% reusable if you clean fingerprints off it with alcohol. My next mission is to try hot glass and ABS. I intend to use PLA as support material for ABS, in which case I can use a single layer PLA raft on glass if ABS does not stick.

But if it was simply an accumulation of ABS we should be able to remove it with acetone.

I am just running a build on my Mendel with a new batch of ABS on some new Kapton and it did not stick. I increased the temperature to 140C and it is sticking well. Maybe 120C is marginal and we just need it hotter for reliability.

I'm torn between a mendel and something more like your hydraraptor.. I'd quite like to be able to mill too and the mendel frame doesn't look sturdy enough for the lateral forces of milling.Building a mendel would take less mental effort though.. why re-invent the wheel?

Probably you have already considered this, Nop, but be careful with heating glass plates. Get a sheet of pyrex if you can as some glass tends to shatter when exposed to a temperature gradient. As a work around, heat the bed up more slowly so that the temp gradient is less sever.

I saw the Reprap project a couple of years ago and parked it in my mind. When I followed up a few weeks ago I saw the progress made. I have just spent all my evenings for the last week reading your entire blog. It's a huge effort and shows where the R&D money in big companies goes.

I've started gathering bits for a Mendel, but will no doubt take a while as I (like many others) my budget is low.

I've also had good initial results. It seemed to stick slightly better than kapton, but this was with an unfinished heater bed.A good source for Kapton and BO-PET is DealExtreme. Their widest rolls are not even above $ 5:http://www.dealextreme.com/details.dx/sku.21359http://www.dealextreme.com/details.dx/sku.21361

I've seen people pay > 100 dollars for the same quanitity of Polymide/Kapton. Too bad D.E. doesn't have these materials as sheets, though.

Demented,Thanks for the tip. I wore goggles for the first test. No sign of it cracking. I think that because it is on an aluminium bed it all heats up uniformly. The only thermal gradient is from bottom to top ,but that is small because glass is a much better conductor than air.

Craig, Thanks.

Erik, Yes I got the tape from DealExtreme but their widest rolls are not very wide. I have paid ~$100 but that was for a roll that was 150mm wide. Unfortunately the rolls are always the same length so wide ones get expensive.

>I do the first layer at 240°C with the bed at 120°C and subsequent layers at 220°C with the bed at 110°C.

What software are you using to make your g-code? I'm trying to do the same with skeinforge with my cupcake, and it looks like I'll have to hack skeinforge to do it. (If I do, I'll try to submit a patch, of course.)

Thanks for all the excellent work! Your blog is a goldmine for the reprap/makerbot community!

How hot can you get the bed? I was thinking of using mendel as a XYZ framework for pick&placing, then soldering (skillet solder method) and then programming (using pogopins on a "printing head"). That'd allow me to essentially mass-custom-produce electronics, other than etching the PCB's.

That does require getting the bed to about 210 or 220 degrees centigrade. So, the main question - can it do that and (other than the temperature) what are the risks?

My current bed can't go that hot because the TO220 resistors are only rated for 150C and I used nylon standoffs. My first design can get hot enough but it didn't heat up and cool down fast enough for SMT reflow. Making it a bit smaller and using more power should make that feasible.

So I just looked up Mylar on Wikipedia, and apparently its another name for PET, (or specifically boPET) so perhaps its no different to what you have already tried? I can't fathom why BestOfferBuy are selling 2 products that are essentially the same material

Yes I have tried PEI / fiberglass laminate but it was too thin to resist warping forces and I didn't find a way to glue it down. I also got an aluminum bed with a PEI coating but that delaminated due the warping force. I just use glass now for ABS and PLA.